Caprolactam has extensive commercial use, including its use in making nylon, such as nylon 6 for example, via condensation polymerization. Existing technology for producing caprolactam, particularly ε-caprolactam, on a commercial scale involves the reaction of cyclohexanone with a hydroxylamine salt to form a cyclohexanone oxime intermediate. Cyclohexanone oxime undergoes Beckmann rearrangement upon treatment with concentrated sulfuric acid to form ε-caprolactam.
Cyclohexanone is typically produced from cyclohexane that has been air oxidized to make a cyclohexanol-cyclohexanone mixture followed by dehydrogenation of the cyclohexanol in the mixture to produce more cyclohexanone. Several impurities are normally present in the cyclohexanol-cyclohexanone mixture obtained from air-oxidation of cyclohexane. Such impurities may include esters, carboxylic acids and cyclohexenone, particularly 2-cyclohexene-1-one. Several methods have been proposed for removing esters and carboxylic acids from cyclohexanol-cyclohexanone mixture.
DE 2,123,184 relates to a saponification method for decomposing the esters in alcohol, especially cyclohexanol, in the residues remaining after cyclohexanol-cyclohexanone distillation. In this way, additional cyclohexanol is obtained that results in a higher yield.
DE 2,650,892 relates to reducing caustic consumption during the treatment of acid and ester by-products by using an alkali hydroxide and carbonate and recycling some of the cyclohexane oxidation off-gas.
Japanese patent J08-019019 relates to eliminating esters and carboxylic acids from mixtures obtained during cyclohexane oxidation in presence of boron products with two step saponification.
Although methods have been taught to remove esters and carboxylic acids from organic mixtures, no method has previously been taught for removing cyclohexenone from organic mixtures of cyclohexenone and compounds such as cyclohexanone or a cyclohexanol-cyclohexanone mixture. If not removed from an organic mixture that is later used in caprolactam production, the cyclohexenone transforms to cyclohexenone oxime, typically 2-cyclohexene-1-one oxime, during the cyclohexanone oxime preparation of the caprolactam production process.
The formation of 2-cyclohexene-1-one oxime is detrimental because it consumes hydroxylamine, a raw material for caprolactam production and may also cause quality problems during polycondensation of the caprolactam during nylon production.